The "defeat device" software apparently lowered carbon emissions from gasoline cars by calculating how much the steering wheel was being turned.

Until now, Porsche's only involvement in the scandal came in the handful of models to which it fitted Audi 3.0-liter V-6 diesel engines in Europe. Only one of those (the Cayenne Diesel SUV) was sold in North America.

A final settlement has been signed for almost half a million Audi and Volkswagen cars that used various 2.0-liter diesel 4-cylinder engines from 2009 through 2015.

But a similar settlement for the separate vehicles from Porsche, Audi, and Volkswagen fitted with the V-6 diesel has yet to be released.

How it worked

During tests on a dynamometer, or rolling road, a car being tested for its emissions has no inputs to the steering.

Reportedly, the Audi transmission being investigated only switched to a regular mode with higher CO2 emissions if the steering wheel was turned more than 15 degrees, as it would be during regular on-road driving.

Porsche responded to questions about that technology by saying that software to detect steering movements is used to improve the car’s performance when driving, and is not related to emissions testing.

The company told Bloomberg it is cooperating fully with the investigation.